3-hydroxypropionate (“3-HP”, CAS No. 503-66-2) has been identified as a highly attractive potential chemical feedstock for the production of many large market commodity chemicals that are currently derived from petroleum derivatives. For example, commodity products that can be readily produced using 3-HP include acrylic acid, 1,3-propanediol, methyl-acrylate, and acrylamide, as shown in FIG. 1. The sum value of these commodity chemicals is currently estimated to exceed several billions of dollars annually in the US. However, the current petrochemical manufacturing techniques for these commodities adverse impact the environment via the pollutants generated and the energy used in their production. Manufacture of these same commodities via the clean, cost-effective, production of 3-HP from biomass will simultaneously reduce toxic waste and substitute renewable feed stocks for non-renewable resources. In addition to the environmental benefits associated with bio-based production of 3-HP, if the production cost of the derived commodities is substantially reduced relative to petroleum-based production, this would make a biorefining industry not only environmentally beneficial but also a very attractive investment.
Previous attempts to produce 3-HP via biological pathways provide product titers which have been low and these processes have required the use of expensive, rich media. Both of these factors limit commercial feasibility and profitability. The use of rich media was necessary due to the toxicity of 3-HP when fermented with the more economical minimal media. For example, in wild type E. coli, metabolic activity is significantly inhibited at levels of 3-HP that are 5-10 times lower than the approximate 100 g/L titer needed for economic feasibility using the more economical minimal media. In fact, toxic effects have also been observed in rich media at product titers which are approximately two times lower than desired titers for commercial feasibility (Refer to FIG. 2). Further, the fermentative pathways reported by other investigators have not addressed and resolved the toxicity mechanisms of 3-HP to the host organisms. Further to issues related to commodity chemical production, which largely relies on petroleum-based starting materials, there is an increasing need to reduce the domestic usage of petroleum and natural gas. The numerous motivating factors for this increasing need include, but are not limited to: pollutant reduction (such as greenhouse gases), environmental protection, and reducing the dependence on foreign oil. These issues not only impact fuel markets, but also the markets of numerous other products that are currently derived from oil. Biorefining promises the development of efficient biological processes allowing for the conversion of renewable sources of carbon and energy into large volume commodity chemicals.
A biosynthetic route to 3-HP as a platform chemical would be of benefit to the public, not only in terms of reduced dependence on petroleum, but also by a reduction in the amount of pollutants that are generated by current non-biosynthetic processes. Because 3-HP is not currently used as a building block for the aforementioned commodity chemicals, technical hurdles must be surmounted to achieve low cost biological routes to 3-HP. These hurdles include the development of a new organism that not only has a metabolic pathway enabling the production of 3-HP, but is also tolerant to the toxic effects of 3-HP thus enabling the sustained production of 3-HP at economically desired levels.
There are numerous motivating factors to reduce the domestic usage of petroleum. These factors include, but are not limited to: 1) the negative environmental impacts of petroleum refining such as production of greenhouse gases and the emission of a wide variety of pollutants; 2) the national security issues that are associated with the current dependence on foreign oil such as price instability and future availability; and 3) the long term economic concerns with the ever-increasing price of crude oil. These issues not only impact fuel markets, but also the multi-billion dollar commodity petro-chemical market
One potential method to alleviate these issues is the implementation of bioprocessing for the conversion of renewable feed stocks (e.g. agricultural wastes) to large volume commodity chemicals. It has been estimated that such bioprocesses already account for 5% of the 1.2 trillion dollar US chemical market. Furthermore, some experts are projecting that up to 50% of the total US chemical market will ultimately be generated through biological means.
While the attractiveness of such bioprocesses has been recognized for some time, recent advances in biological engineering, including several bio-refining success stories, have accelerated interest in the large scale production of chemicals through biological routes. However, many challenges still remain for the economical bio-production of commodity chemicals. These challenges include the need to convert biomass into usable feed stocks, the engineering of microbes to produce relevant chemicals at high titers and productivities, the improvement of the microbes' tolerance to the desired product, and the need to minimize the generation of byproducts that might affect downstream processes. Finally, the product must be economically competitive in the marketplace.
The contributions of bioprocessing are expected to grow in the future as existing biological methods become more efficient and as new bioprocesses are developed. A recent analysis by the U.S. Department of Energy identified a list of the Top Value Added Chemicals from Biomass that are good candidates for biosynthetic production. Eight of the top value added chemicals were organic acids, including 3-hydroxypropionic acid (3-HP). As depicted in FIG. 1, 3-HP is considered to be a platform chemical, capable of yielding valuable derivative commodity chemicals including acrylic acid and acrylic acid polymers, acrylate esters, acrylate polymers (plastics), acrylamide, and 1,3-propanediol. Presently, these high value chemicals are produced from petroleum.
One method to efficiently generate 3-HP by a bioprocess approach would be the microbial biosynthesis of renewable biomass sugars to 3-HP. According to the DOE Report (Werpy, T.; Petersen, G. Volume 1: Results of Screening for Potential Candidates from Sugars and Synthetic Gas. Oak Ridge, Tenn., U.S. Department of Energy; 2004. Top Value Added Chemicals from Biomass), a number of factors will need to be addressed, including: identifying the appropriate biosynthetic pathway, improving the reactions to reduce other acid co-products, increasing microbial yields and productivities, reducing the unwanted salts, and scale-up and integration of the system. Additionally, as noted above, it is critical to engineer the microbial organism to be tolerant to the potential toxicity of the desired product at commercially significant concentrations.
The production of acrylic acid from 3-HP is of particular interest because of the high market value of acrylic acid and its numerous derivatives. In 2005, the estimated annual production capacity for acrylic acid was approximately 4.2 million metric tons, which places it among the top 25 organic chemical products. Also, this figure is increasing annually. The demand for acrylic acid may exceed $2 billion by 2010. The primary application of acrylic acid is the synthesis of acrylic esters, such as methyl, butyl or ethyl acrylate. When polymerized, these acrylates are ingredients in numerous consumer products, such as paints, coatings, plastics, adhesives, dispersives and binders for paper, textiles and leather. Acrylates account for 55% of the world demand for acrylic acid products, with butyl acrylate and ethyl acrylate having the highest production volumes. The other key use of the acrylic acid is through polymerization to polyacrylic acid, which is used in hygiene products, detergents, and waste water treatment chemicals. Acrylic acid polymers can also be converted into super absorbent materials (which account for 32% of worldwide acrylic acid demand) or developed into replacement materials for phosphates in detergents. Both of these are fast growing applications for acrylic acid.
Today, acrylic acid is made in a two step catalytic oxidation of propylene (a petroleum product) to acrolein, and acrolein to acrylic acid, using a molybdenum/vanadium based catalyst, with optimized yields of approximately 90%. It should be noted that several commercial manufacturers of acrylic acid are exploring the use of propane instead of propylene. The use of propane is projected to be more environmentally friendly by reducing energy consumption during production. However, propane is petroleum based, and while its use is a step in the right direction from an energy consumption standpoint, it does not offer the benefits afforded by the bioprocessing route.
In addition to acrylic acid, acrylates, and acrylic acid polymers, another emerging high value derivative of 3-HP is 1,3-propanediol (1,3-PD). 1,3-PD has recently been used in carpet fiber production for carpets. Further applications of 1,3-PD are expected to include cosmetics, liquid detergents, and anti-freeze. The market for 1,3-PD is expected to grow rapidly as it becomes more routinely used in commercial products.
Pursuing a cleaner, renewable carbon source route to commodity chemicals through 3-HP will require downstream optimization of the chemical reactions, depending on the desired end product. 3-HP production through bioprocesses directly, or through reaction routes to the high-value chemical derivatives of 3-HP will provide for large scale manufacture of acrylic acid, as well reduction of environmental pollution, the reduction in dependence on foreign oil, and the improvement in the domestic usage of clean methods of manufacturing. Furthermore, the products produced will be of the same quality but at a competitive cost and purity compared to the current petroleum based product.
Thus, notwithstanding various advances in the art, there remains a need for methods that identify and/or provide, and compositions directed to recombinant microorganisms that have improved 3-HP production capabilities, so that increased 3-HP titers are achieved.